Liquid superacids, e.g., HF/BF.sub.3, are use to catalyze reactions such as the alkylation of paraffins and the carbonylation of aliphatic hydrocarbons, see, WO 98/50336. However, the use of liquid super acids such as HF/BF.sub.3 are not environmentally friendly and thus their replacement has received considerable attention. In the search for such replacement a family of compounds, known as ionic liquids, is receiving attention because they can act as both catalysts and solvents and have no measurable vapor pressure.
Ionic liquids are sometimes referred to as molten salts, but they are not molten salts in the sense of molten sodium chloride. Ionic liquids have melting points below room temperature and have liquid ranges of as much as 300.degree. C. compared to the 100.degree. C. liquid range for water. One example is 1-ethyl-3-methylimidazolium chloride-aluminum chloride, which is abbreviated as (emim)Cl--AlCl.sub.3. This ionic liquid is liquid from about -100.degree. C. to about 200.degree. C. depending on the amount of (emim)Cl and AlCl.sub.3. When the molar percentage of AlCl.sub.3 is 65%, the melting point is -96.degree. C.
The cation in the ionic liquid is an organic cation such as (emim).sup.+ while the anions are inorganic anions such as the anions of AlCl.sub.3 (AlCl.sub.4.sup.-, Cl.sup.-, Al.sub.2 Cl.sub.7.sup.-). The organic cations account for the low melting points, while the chemical properties are determined mostly by the anions. Finally, depending on the relative amounts of the inorganic anions, the ionic liquid can be basic, neutral or acidic. A review of ionic liquids can be found in Chemical and Engineering News, Mar. 30, 1998, pp. 32-37 and K. R. Seddon, "Ionic Liquids for Clean Technology: An Update," Molten Salt Forum Vols. 5-6 (1998) pp. 53-62, Trans Tech Publications, Switzerland.
WO 95/21806 discloses the alkylation of aromatics by an olefin using an ionic liquid as the catalyst. Specifically, the alkylation of benzene with ethylene using a (emim)Cl--AlCl.sub.3 ionic liquid catalyst with 67 wt. % AlCl.sub.3 and 33 wt. % (emim)Cl. U.S. Pat. No. 4,554,383 discloses a process to prepare p-tolualdehyde by reacting toluene and CO in the presence of a "melt" catalyst composed of a N-alkyl-pyridinium halide and aluminum chloride. WO 00/15594 discloses reacting an alkyl aromatic compound with CO in the presence of an acidic ionic liquid to form an alkyl aromatic aldehyde.
Although the carbonylation of aromatics (or olefins) is fairly facile, the carbonylation of saturated hydrocarbons is extremely difficult. The fundamental problem in the direct carbonylation of saturated hydrocarbons is the high stability of the C--C and C--H bonds. In view of the high stability of these bonds, attempts to directly convert saturated hydrocarbons to hetero organic molecules have met with few successes. For example U.S. Pat. No. 2,874,186 discloses a process for reacting carbon monoxide with normal paraffins, isoparaffins and naphthenes to produce ketones, acids and esters. The process involves placing the isoparaffin in a reactor with hydrogen fluoride and boron trifluoride (HF/BF.sub.3) and carbon monoxide under high pressures. The products, which were obtained from this process, were ketones and carboxylic acids. U.S. Pat. No. 2,346,701 discloses preparing organic oxygen-containing compounds such as ketones and acids by reacting propane with carbon monoxide using an anhydrous aluminum halide catalyst, e.g., aluminum chloride. U.S. Pat. No. 3,356,720 discloses preparing oxygenated organic compounds by reacting saturated hydrocarbons with carbon monoxide using a Freidel-Crafts catalyst and a tertiary alkyl, phenyl alkyl or phenyl carbonyl halide. Both ketones and carboxylic acids are produced. It is also disclosed in WO 98/50336 that branched aliphatic hydrocarbons can be converted to branched aliphatic ketones by reacting the hydrocarbons with carbon monoxide at high pressures and super acidic conditions. The super acidic conditions are produced by the combination of a protic acid such as HF and a Lewis acid such as BF.sub.3. The reaction is carried out at temperatures of about 0.degree. C. to about 35.degree. C. and pressures of about 10 to 200 atmospheres.
All of the above references disclose the use of superacids, for carbonylation, which are corrosive, volatile and environmentally harmful. In the pursuit of an environmentally green process for the carbonylation of saturated hydrocarbons, applicants have developed a process using ionic liquids. The process involves reacting the hydrocarbon with carbon monoxide in the presence of an acidic ionic liquid to produce an oxygenated saturated hydrocarbon. The ionic liquid serves both as the catalyst and the solvent. One example of an ionic liquid is AlCl.sub.3 (n-butylpyridinium chloride) with a ratio of AlCl.sub.3 :(n-butylpyridinium chloride) of 64:36 by weight.